Transcript Document

Nanoscience and
Nanotechnology
Ideas for Educators
Why teach nano?
• An active area of research – science “in
real time”
• Multidisciplinary
• Interesting applications
• Hooks to basic science
• “Extra-scientific” implications
Challenges
• Possibly unfamiliar subject matter
– True boundaries of knowledge may not be
clear except to (some) experts!
• Multidisciplinary
• Centrality of quantum physics
Workshop Goals
•
•
•
•
Subject-matter orientation
Some ideas for teaching
Lab exercises
Pointers to additional resources
A Short History of
Atomic Ideas
• Earliest formulation due to the Greeks
– “atom” = a-tom, Greek for “not divisible”
– Pre-scientific
• In Rome: Lucretius (1st century B.C.)
• Out of favor (along with much other
learning and scholarship) for almost
2000 years
The Modern Era
• 18th century: Re-introduced by Daniel
Bernoulli, Roger Boscovitch
• Dalton: Laws of Definite and Multiple
Proportions
• Kinetic Theory
– Clausius, Maxwell, Boltzmann; 19th c.
• Brownian Motion
– Brown, Einstein, Perrin; early 20th c.
Democritus (~460–380 B.C.)
• “Thought experiment”: Subdivide a
piece of gold
– Each part is still gold after every division
– Claimed there must be some limit; matter is made
of particles that cannot be further divided
• These “atoms” move endlessly in all
directions in “the void”
• Determinism?
– A relief from capricious and cruel gods
Lucretius (~95–55 B.C.)
• Roman philosopher and poet; student of
Epicurus
• Manuscript De Rerum Natura (On the
Nature of Things) re-discovered in late
14th century
• Allegedly driven mad by a “love potion”
given to him by his wife, committed
suicide
…clothes hang above a surf swept shore
grow damp; spread them in the sun they dry again.
Yet it is not apparent to us how
the moisture clings to the cloth, or flees the heat.
Water, then, is dispersed in particles,
atoms too small to be observable.
…
For surely the atoms did not hold council, assigning
order to each, flexing their keen minds
with questions of place and motion and who goes where.
But shuffled and jumbled in many ways, in the course
of endless time they are buffeted, driven along,
chancing upon all motions, combinations.
At last they fall into such an arrangement
as would create this universe…
–Lucretius, De Rerum Natura
Early Objections
• Some quasi-religious or philosophical,
of course, but some “scientific” ones as
well
• How can atoms continue moving for all
time without stopping?
– According to Aristotle, moving objects come to a
halt unless something intervenes to keep them
moving
Early Objections
• The “void” in which atoms supposedly
move cannot exist, according to some
philosophers:
– For anything to exist it must have a name, which
refers to something rather than nothing
– Since “nothing” cannot have such a name, it
therefore cannot exist
Atomic Theory
If, in some cataclysm, all of scientific knowledge were to be
destroyed, and only one sentence passed on to the next generation
of creatures, what statement would contain the most information in
the fewest words? I believe it is the atomic hypothesis … that all
things are made of atoms – little particles that move around in
perpetual motion, attracting each other when they are a little distance
apart, but repelling upon being squeezed into one another. In that one
sentence, there is an enormous amount of information about the
world, if just a little imagination and thinking are applied.
– Richard Feynman
• Key strands of evidence from both
physics and chemistry…
John Dalton (1766-1844)
• British chemist and physicist
• The foremost proponent of
atomic theory
– all elements are composed of
indestructible atoms
– all compounds are simple
combinations of atoms
• Law of Multiple Proportions
(1803)
Dmitri Mendeleyev
• One of several to see
the patterns in the
properties of the
elements
• Predicted the existence
(and properties) of
several then unknown
elements!
Discovery of the Elements
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Mendeleyev's Periodic Table
What is Heat?
• A central part of the mystery
• Majority view around 1800: heat is a
fluid, called caloric
• It flows from hotter bodies to colder
ones
– E.g. we drop a hot horseshoe in water; caloric
flows from the shoe into the water, cooling the
shoe and heating the water
• Mysterious, undetectable (?)
Kinetic Theory
• In the atomic theory, heat has to do with
the (random) motion of the particles
– Faster speeds on average means higher
temperature
• Rudolf Clausius: The Kind of Motion We
Call Heat (1857)
• A consequence: There is a lowest
temperature! (Davy)
Kinetic Theory
• A description of matter
in terms of randomly
moving particles
(atoms)
– Response to Aristotle (how
can atoms stay moving
forever?) given by Newton
Kinetic Theory
• For a gas, for example
– Pressure is due to the
particles colliding with
the container walls
– Temperature is a
measure of the
average speed of the
particles
Ludwig Boltzmann (1844-1906)
• Professor in Vienna
– Also Graz, Munich, Heidelberg,
Berlin, Leipzig
• Brings kinetic theory onto a
firm foundation: “statistical
mechanics”
– Independently: J. W. Gibbs
• Ongoing battles with Ernst
Mach and others over atomic
and kinetic theory
The Conflict With Mach
• Mach’s view: “Positivism” (a particularly
strong version!)
• Science should be based only on
observable facts
– The pressure exerted by a gas on the walls of its
container is an acceptable fact
– “Explaining” that pressure in terms of invisible
particles is unacceptable, since the particles
cannot be seen
The Conflict With Mach
• Heat is also a primary phenomenon
– Explaining it in terms of the motion of unseen
particles is unacceptable
• For Mach, science is more description
than understanding
– Just study the relation between T and P, e.g. how
does P change as T is increased? Then make a
catalog of results…
Boltzmann’s View
• Truth in science need not be seen
directly, but is what can be consistently
inferred from observations
– Even though we cannot see atoms directly, the
atomic hypothesis makes predictions, e.g. about
how P changes if T is increased
– If those predictions are confirmed by experiment, it
provides support to the atomic hypothesis
Boltzmann’s View
• If many predictions that follow from the
atomic hypothesis are confirmed, we
may believe in the existence of atoms
– In effect, we “see” atoms by their effects
– Not really so different from “seeing” anything!
• This is the modern attitude
• Plus, today we can “see” atoms directly!
X-Ray Diffraction
• X-rays have wavelengths
comparable to atomic
sizes (~10–10 m)
• Can “see” atoms and
molecules by bouncing
X-rays off them
• Crystals and molecules
reflect X-rays in patterns
depending on their
structures
X-ray diffraction pattern of DNA
Electron Microscope Images
•
Xenon on Nickel
Iron on Copper
Boltzmann and Philosophy
• After Mach retired, Boltzmann returned
to Vienna and was given Mach’s
philosophy course to teach
• These lectures became famous, in part
for their attacks on various philosophies
and philosophers
Boltzmann and Philosophy
• Proposed title of a talk for the VPS:
Proof that Schopenhauer is a stupid,
ignorant philophaster, scribbling nonsense
and dispensing hollow verbiage that
fundamentally and forever rots people’s
brains
(These were actually Schopenhauer’s own
words regarding Hegel!)
Boltzmann’s Death
• Moody, depressed,
highly sensitive to
criticism
• Suicide, (perhaps) due
to despair at slow
acceptance of his ideas
Brownian Motion
• Discovered in 1828 by
Robert Brown, a botanist
• Observed that microscopic
pollen grains suspended in
a liquid move around
erratically, even though the
liquid itself has no
observable motion
Explanation
• The grains are being jostled and
buffeted by unseen atoms
• In 1905, Albert Einstein calculated the
details of this process and made several
predictions
– E.g. how fast a collection of pollen grains should
spread out
• Quickly confirmed by experiments
• Convinced remaining skeptics
Einstein’s “Miraculous Year”
• In addition to the paper on
Brownian motion, AE
published two other papers
in 1905:
– The special theory of
relativity (including E = mc2)
– An explanation of the
“photoelectric effect”
• Early quantum ideas
• Won him the Nobel prize in
1921
Recap: Why Atoms?
• Chemical combination rules (Dalton)
• Success of atomic/kinetic theory in
describing behavior of matter
• Brownian motion
• X-ray diffraction